This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A255558 #7 Apr 19 2015 00:52:58 %S A255558 1,2,3,5,4,7,6,9,11,8,12,16,22,29,10,14,37,17,13,46,56,18,23,67,30,38, %T A255558 79,92,106,121,15,20,137,47,24,154,172,19,57,191,68,25,211,232,254,31, %U A255558 80,277,39,48,301,326,93,107,352,122,138,379,407,436,466,497,21,27,529,155,58,562,596,32,173,631,192,26 %N A255558 Inverse permutation to A255557. %H A255558 Antti Karttunen, <a href="/A255558/b255558.txt">Table of n, a(n) for n = 1..10000</a> %H A255558 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A255558 a(n) = (1/2) * ((c+r)^2 - r - 3*c + 2), where r = A255559(n), and c = A255560(n). %o A255558 (Scheme) (define (A255558 n) (let ((row (A255559 n)) (col (A255560 n))) (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2)))) %Y A255558 Inverse permutation: A255557. %Y A255558 Cf. A255556, A255559, A255560. %K A255558 nonn %O A255558 1,2 %A A255558 _Antti Karttunen_, Apr 14 2015